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Earthquakes: Processes, Occurrence, and Impact

Learn about earthquakes, fault types, seismic wave production, and how faults relate to earthquake risk assessment. Discover where earthquakes occur, their relationship to plate boundaries, and why intraplate earthquakes are significant. Understand the deadliest earthquakes on record and the factors affecting earthquake intensity. Explore earthquake-prone areas and the influence of population density, land use, and building construction on seismic hazards.

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Earthquakes: Processes, Occurrence, and Impact

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  1. Earthquakes and Related Phenomena

  2. Earthquake Web Resources http://earthquake.usgs.gov/

  3. Deadliest Earthquakes on Record

  4. Introduction to Earthquakes MsEarthquakes/year 8.5 - 8.9 0.3 8.0 - 8.4 1.1 7.5 - 7.9 3.1 7.0 - 7.4 15 6.5 - 6.9 56 6.0 - 6.4 210 • ~1 million earthquakes a year • Change of 1 Mw = ~30 X energy • Great earthquakes; Ms >8 • Major earthquakes; Ms=7-7.9 (widespread damage) • Moderate earthquakes: Ms=6 (considerable damage) • Population factors: density, land use, and building construction

  5. Where do earthquakes occur? Plate boundaries, but not only – intraplate earthquakes are also common

  6. Earthquake Occurrence • Most occur along plate boundaries. • Loma Prieta (1989) • North Ridge (1994) • Intraplate earthquakes • Can be large and quite damaging. • New Madrid zone is a foundered rift zone • Salt Lake City and south into New Mexico • Charleston, S.C.

  7. Largest US Earthquakes

  8. Relationship of Earthquakes to Faults

  9. Earthquake Processes • Faults, Folds & Concealed Faults, and Movement • Fractures • Faults are fractures or systems along which rocks have been displaced • Model: brick -bungee cord on a winch; sand paper • Joints are fractures and fractures systems along with rocks have NOT been displaced • Slip rate aver. long-term rate of movement ( mm/yr or m/1000 yrs); risky measurement • Seismic waves produced by rupture • Faults-seismic sources; used to evaluate the earthquake risk in a given area

  10. Earthquake Processes • Fault types • Strike-slip faultsonly have horizontal displacement (right-or left-lateral) • Normal faultsoccur where the hanging wall moves down with respect to the foot wall; results in crustal extension • Reverse faultsoccur when the hanging wall moves up with respect to the foot wall; results in crustal shortening; low fault plane angle ( less than 45°)= thrust fault • Oblique faultshave both horizontal and vertical components • Buried faultsmay cause earthquakes and have to surface expression

  11. Faults – Understanding Strike and Dip

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